由于长时间在强烈的热带阳光下活动,这种草鼠进化出了两种不同的保护方式对抗太阳的紫外线照射。首先,像生活在世界这一地区的人类,草鼠的皮肤里含有很多黑色素。
第二,非常奇特的是,这种老鼠的头骨和皮肤之间有一层黑素着色组织。这个独特的帽子为草鼠和其他三种非洲鼠,像白天活动的啮齿类动物,提供了额外的保护。科学家发现另外唯一一种具有相同头骨适应性的物种是生活在中美洲热带地区的白色尾皮蝠。尽管这种蝙蝠白天睡觉,它们睡觉时身体蜷缩把头暴露在日光下。
生词摘录:
1. 赤道 名词 equator
2. 夜行的 形容词 nocturnal
3. 树丛繁盛的 形容词 scrubby
4. 条纹 名词 stripe
5. 花栗鼠 名词 chipmunk
6. 紫外线的 形容词 ultraviolet
7. 黑色素 名词 melanin
8. 色素 名词 pigment
9. 啮齿类动物 名词 rodent
10. 头骨 名词 skull
英文译文：
Human populations near the equator have evolved over many generations to possess dark skin due to long-term exposure to the fiercest sun rays. A similar phenomenon also occurred in other parts of the animal kingdom. The African grass mouse is a good example. Most mice are nocturnal, but the African grass mouse is active during daylight hours. This means that it spends its days searching for food in the semi-dry bushes of scrubby habitats in eastern and southern Africa. Its furry, stripy exterior resembles that of a chipmunk, which helps it blend in with its environment.
Because it spends a lot of time in the intense tropical sun, the grass mouse has also evolved two separate safeguards against the sun's ultraviolet radiation. First, like the population of humans in this region of the world, the skin of the grass mouse contains lots of melanin, or dark pigment.
Second, and quite unusually, this mouse has a layer of melanin-pigmented tissue between its skull and skin. This unique cap provides an extra measure of protection for the grass mouse and three other types of African mouse, like rodents that are active during the day. The only other species scientists have identified with the same sort of skull adaptation is the white tent-making bat of the Central American tropics. Although these bats sleep during the day, they do so curled up with their heads exposed to the sun.
